Rocky Shore Community Structure Research Articles

Biogeographic drivers of distribution and abundance in an alien ecosystem engineer: Transboundary range expansion, barriers to spread, and spatial structure

AbstractAimBiogeographic boundaries can act as either weak or strong barriers to the spread of species undergoing distributional change. Once a novel species spreads across a boundary, it can have a substantial impact on the ecosystem, for instance by competing with local species, and, over the long‐term, re‐engineer the ecosystem. Marine biogeographic regions are clearly defined on the coast of southern Africa and we tested the influence of their boundaries on the spread and spatial structure of an alien ecosystem engineer.LocationSouthern Africa.TaxonAn invasive mussel, Mytilus galloprovincialis.MethodsRecords of M. galloprovincialis were compiled into a database to determine its decadal patterns of spread across multiple bioregions. Distribution and abundance (estimated using density and semi‐quantitative abundance scale [ACFOR]) of this mussel were surveyed to determine patterns in spatial structure across bioregions. In addition, we compared the size structure of populations at the eastern margins of its range with those of larger populations nearer the range centre.ResultsInitial breaching of biogeographic boundaries was associated with rapid spread, but other boundaries encountered decades later acted as barriers to further spread. Across >2,800 km of coast, spatial autocorrelation was observed in densities (low and mid shore levels) and in ACFOR abundances. Repeating spatial patterns in densities and ACFOR abundance were detected at scales of 120–160 km and of 400–990 km. Considerable effort was required to detect populations at the absolute eastern limits of its distribution.Main conclusionDetection of spatial structures at multiple scales suggests that ecologically determined processes regulate abundance at both intra‐bioregional and inter‐bioregional scales, which may help tease apart the historic and contemporary consequences of interspecific interactions on the structure of rocky shore communities. This study demonstrates the influence of biogeography in driving temporal patterns of spread and spatial structure on the distribution and abundance of an invasive species.

Long-term fluctuations in intertidal communities in an Irish sea-lough: Limpet-fucoid cycles

Long-term cyclical changes in rocky shore community structure were documented over two decades at sheltered shores in Lough Hyne Marine Reserve, County Cork, Ireland. Three peaks of abundance were recorded for the limpet, Patella vulgata (1990-5, 2002-6 and 2010-14) with oscillations that varied in amplitude and frequency among sites. The cover of the fucoid Fucus vesiculosus varied inversely with limpet abundance and showed the strongest negative correlation with a lag time of 0–2 years. The species complex Fucus spiralis/guiryi showed a weaker correlation with a lag time of 1–2 years. Two other fucoid species showed no such negative correlations despite their close proximity to limpets within the lough's compressed tidal range. There was no relationship between overall barnacle cover (dominated by Austrominius modestus) and the limpet-fucoid cycles, suggesting that the shelter provided by A. modestus for algae to escape from limpet grazing pressure may not be necessary for these cycles to occur on wave-sheltered shores.

General spatial spectral variation in rocky intertidal communities from three biogeographical regions

Aim Understanding general spatial patterns of multiple species is a central aim of biogeography. Spatial analyses of coastal marine assemblages have shown an emergent pattern in that the variability in population abundances increases with increasing spatial scale of observation; i.e. a “red” spectrum of variation in population abundances. However, the generalization of these patterns to other ecological levels and across biogeographical regions remains unexplored. Here, we evaluate the consistency of a reddened relationship between the scale of observation and the variance in ecosystem properties in sessile intertidal rocky-shore assemblages across three biogeographical regions. Location Replicate sites located in temperate (southern-central Chile), sub-Antarctic (Chilean South Patagonia) and Antarctic (West Antarctic Peninsula) regions. Methods A total of 16,225 photo-quadrants were used to analyse local patterns of total community cover, bare substratum, total algal cover and total invertebrate cover. We used spectral analyses in which the spatial variance of each property was decomposed along a gradient of increasing distances between observations. Cross-semivariograms were used to analyse the spatial covariation of dominant taxa. Results The analysed ecosystem properties showed a general reddened spectrum of variation that resembled patchy configurations of local communities. Additionally, cross-semivariance analyses indicated mainly negative relationships of covariation between the abundances dominant sessile species at each site, suggesting a general trend of spatial asynchrony between competing species. Main conclusions To the best of our knowledge, this is the first study showing a general reddened pattern of spatial variation in relevant ecosystem-level properties across the Pacific shore of South America, southern Patagonia and West Antarctic Peninsula. These patterns reflect the result of multiple biotic and abiotic processes that interact across spatial scales. In particular, we suggest that processes that generate spatial asynchrony between competing species, such as compensatory dynamics, are relevant to maintain the spatial structure of rocky-shore communities.

Biogeographical patterns of rocky shore community structure in south‐east Australia: effects of oceanographic conditions and heat stress

AbstractAimEnvironmental variability can be a major driver of large‐scale patterns of distribution and abundance and, within the marine environment, benthic community structure is usually thought to reflect several oceanographic processes and coastal morphological features. The aim of this study was to quantify spatial and temporal variability in large‐scale rocky intertidal community structure along the south‐east coast of Australia and ask whether these are associated with variation in sea‐surface temperatures, chlorophyll‐a concentration, heat stress and coastal geomorphology.LocationRocky intertidal shores of south‐east Australia spanning > 1750 km, 13° of latitude (26°24′23″ S to 39°07′47″ S) and known biogeographical barriers.MethodsFrom 2009 to 2011 one‐thousand and twenty photoquadrats located within the midshore region of 17 rocky shores (20 quadrats site−1 year−1) were used to estimate spatial and temporal variability in the percentage cover of dominant benthic invertebrates and macroalgae. We used satellite data to generate annual estimates of nearshore sea‐surface temperatures (SST) and chlorophyll‐a concentrations ([Chl‐a]) and a meteorological model to estimate heat stress during summer low‐tides.ResultsNon‐metric multidimensional scaling and cluster analysis revealed a strong and consistent biogeographical break in rocky intertidal community structure between southern and eastern sites. Nearshore oceanographic conditions and summer heat stress did not appear to influence this discontinuity as abundances of functional groups (filter‐feeders, grazers and macroalgae) generally did not vary in response to geographical patterns of SST, [Chl‐a] or mean daily maximum air temperatures during low‐tide. At the species level, however, the distribution and abundance of several species varied with nearshore SST and [Chl‐a] including the barnacle Tesseropora rosea and limpets within the genus Patelloida, respectively.Main conclusionsWe found no evidence of strong bottom‐up effects on rocky intertidal functional group abundance. This was somewhat expected because bottom‐up effects in regions characterized by persistent downwelling are generally weak or non‐existent. Instead, broad‐scale patterns of community composition were best explained by coastal geomorphology. This study provides an important and necessary comparison for the role of broad‐scale environmental variability in structuring marine benthic communities within downwelling rather the more commonly reported upwelling systems.

Pending possible establishment of Littorina littorea in the Pacific: to know the remedy, know thine enemy

The number of human-mediated marine introductions is constantly growing globally, and whenever a non-indigenous species survives the most critical filters it encounters, such as tolerance to conditions during transport and survival in the new habitat with novel species interactions (Elton 1958; Mack et al. 2000; Lenz et al. 2011; Sareyka et al. 2011), it may become permanently established and in the worst case proceed to impose clearly negative impacts on its new surroundings. One such introduction may be exemplified by the common periwinkle, Littorina littorea, which supposedly was introduced to the NW Atlantic from Europe in the 1840s as a food source or in rock ballast (Chapman et al. 2007). Now, L. littorea constitutes one of the most abundant mollusks in its invaded NE American range with extensive ecological effects such as reduced recruitment of algae and invertebrates as well as generally altered rocky shore community structure and diversity (see Harley et al. 2013 for references, and Diaz et al. 2012 for more on its effects in its native European range). During the past few decades, L. littorea has also appeared in several locations on the North American Pacific coast (see Harley et al. 2013 for references), although it does not yet seem to be self-recruiting (Chang et al. 2011). This time, the main vector is probably the export of live seafood followed by people’s diverse reasons (ethical and religious considerations or a personal desire to establish a harvestable resource) for releasing living snails (Harley et al. 2013). Why are then some introductions immediately successful, while others are not? Understanding the factors restricting the establishment of a species is arguable one of the holy grails of invasion biology, and the unique opportunity to focus on a species that seems likely to establish, but has not yet done so, is very exciting from an strictly ecological point of view (e.g. Stachowicz et al. 2002), despite all the possible downsides associated with a permanent establishment. In their original article, Harley et al. (2013) provides a comprehensive case study of the current status for L. littorea in Vancouver, where L. littorea has been found only at a couple of sites, without detectable community impact, this far. Whenever encountered, the species has been eradicated by the authors and co-workers, and to date, L. littorea has not been found again during repeated revisits over the past 1.5 years. Regarding the collected individuals, their morphology and the presence of possible hitchhikers were examined and compared to market snails. The laboratory examination indicated that the field specimens likely originated from the live seafood trade and that cooccurring organisms, living on the gastropod shells and as gut parasites, could still be introduced even if a L. littorea introduction would fail. A set of experiments, focusing on potential future success and impact of L. littorea, like comparing its grazing effects with those of a native gastropod, determining its survival under low salinity and its susceptibility to native predators, rendered significant and interesting results. L. littorea had a similar dietary preference as the native gastropod Chlorostoma funebralis suggesting possible competition. L. littorea was also capable of surviving at seasonal low salinity in the area. Most Communicated by U. Sommer.

Ecological subsidies to rocky intertidal communities: Linear or non-linear changes along a consistent geographic upwelling transition?

Through bottom–up inputs and larval transport, benthic–pelagic links can have an important effect on benthic community structure. Recent work on community structure of northeast Pacific rocky shores has focused on latitudinal differences in recruitment of intertidal invertebrates as a driver of variation in community structure. Recruitment differences are associated with a transition in upwelling near Cape Blanco in southern Oregon. Here we examine the transition in recruitment along an unstudied gap on the northern California and Oregon coasts, document a latitudinal gradient in bottom–up factors, and examine if major coastal promontories associated with upwelling plumes potentially separate benthic–pelagic coupling into regions. We monitored the recruitment of intertidal invertebrates, chlorophyll a concentrations in coastal waters, and the growth rates of mussels at numerous sites along the northern California and Oregon coasts. The transition in recruitment of intertidal invertebrates from north to south changed from very high levels north of Cape Blanco, to intermediate levels between Capes Blanco and Mendocino, to very low levels south of Cape Mendocino. The specific shape of the recruitment cline varied among species. Chlorophyll a concentrations and mussel growth rates were higher north of Cape Blanco than south of Cape Blanco, indicating that bottom–up factors may also drive regional differences in rocky shore community structure. Distinctive timing between regions of recruitment and plankton pulses suggests that benthic–pelagic coupling may be somewhat independent between these regions, which are separated by major coastal promontories. Our results highlight the large variability in spatially coupled ecosystems along the northern California and Oregon coasts that drive the latitudinal gradient in rocky shore community structure in the northeast Pacific.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

Human activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

AbstractHuman activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

Wave exposure indices from digital coastlines and the prediction of rocky shore community structure

Topographical wave exposure indices allow objective assessment of the degree of wave action at coastal sites. We present a grid-based method for rapidly calculating indices at fine spatial resolutions along whole coastlines, and evaluate the power of candidate indices in predicting composi- tion of rocky shore communities. The method has 3 stages: (1) a grid is created from a vector-based digital coastline using geographical information systems (GIS) software; (2) for every coastal cell, wave fetch is determined as the distance to the nearest land cell in 16 angular sectors, using coarse-, medium- and fine-resolution searches of the surrounding cells up to a distance of 200 km; (3) wind energy (average wind speed and propor- tional occurrence) in each sector is calculated for nearby coastal sites. We calculated the average fetch in each sector ( F) and the sum of products of fetch and wind energy ( W) . A total of 57 species were surveyed at 185 sites in west Scotland for determination of trends with wave indices. Average wave fetch with a 200 m scale grid explained > 50% of the variation in the first principal compo- nent of the species-sites abundance matrix, with shore extent explaining another 10%. Incorporating wind data in the indices had a negligible effect on predictive power. Species diversity explained 61% of the variance in the second principal component and declined from low to high pelagic primary pro- ductivity. Separating direct physical effects from biological effects, such as food supply or grazing could potentially help us better understand the pro- cesses structuring biological communities on rocky shores.

Effects of grazer identity on the probability of escapes by a canopy-forming macroalga

Through their grazing activities limpets have an important role in controlling macroalgal abundance and as a result the structure and dynamics of rocky shore assemblages. Using two congeneric limpet species, with different biogeographic distributions, and whose ranges are expected to alter with climatic warming, we separated the magnitude of their grazing activity over time and the subsequent consequence for macroalgal growth. The northern/boreal limpet, Patella vulgata (L.), consistently grazed more than the southern/lusitanian limpet, P depressa (Pennant), particularly during spring and summer when P depressa was reproductively active. Individuals of Fucus vesiculosus (L.) that settled during this time were able to grow to a size where they escaped the grazing activities of P. depressa, resulting in mature F vesiculosus being present in all P. depressa treatments. In contrast, P vulgata, which was not reproductively active during this period, exhibited no reduction in its grazing activity and prevented macroalgae from growing in experimental treatments. It therefore appears that P. vulgata has a stronger role, than P depressa, in controlling macroalgal abundance on shores of southwest Britain. We present a conceptual model highlighting the direct and indirect interactions between these two limpet species and F. vesiculosis. If as predicted, under current warming scenarios, P depressa becomes the dominant limpet on shores of southwest Britain there will be subsequent changes in rocky shore community structure and ecosystem functioning. Our research emphasises that even closely related species with similar ecological niches can exhibit different behaviours that fundamentally alter their biological interactions with other organisms leading to idiosyncratic responses to predicted changes in climate. (C) 2007 Elsevier B.V All rights reserved.

SEASCAPE-DEPENDENT SUBTIDAL–INTERTIDAL TROPHIC LINKAGES

In this study, we test in southern New Zealand a conceptual model of food web linkage that is seascape dependent, which can explain some of the variability in rocky shore community structure among sites and coasts. Using a comparative-experimental approach at local and distant sites we demonstrate that mobile subtidal predators (fish and crabs) can exert strong predation pressure on small mussels in the low tidal zone, but only in sites where the seascape includes subtidal reefs. On intertidal benches with adjacent subtidal reefs (+SR), 60-100% of small (5-15 mm) transplanted mussels were removed within a day from experimental tiles on the low shore when unprotected from predation, compared to fully caged controls that had approximately 100% survival over several months. In partial cages that exclude fish but not crabs, survivorship was intermediate. In contrast, on benches without subtidal reefs (-SR) 40-100% of mussels survived for months, even if unprotected. This difference is expressed in lower cover (0-60%) of mussels on rocks at +SR benches compared to -SR benches (70-99%). The central to northern west coast of the South Island is composed mostly of -SR benches, and predation on small mussels there was low and similar to the -SR benches on the east coast, whereas the +SR benches on the east coast had much greater predation. This contrasts to other studies in New Zealand that examined only predation on larger mussels by seastars and concluded that predation is strong on the west coast and weak on the east coast. Excluding large predators from low-shore areas with new recruits for a year in one +SR site showed longer-term predation effects on their abundance and cover. Short-term sampling at the east coast sites showed that mussel settlement was greater in -SR compared to +SR sites, providing some evidence that seascapes may also affect settlement. Overall, predation depended on the local seascape and ultimately affected community structure via suppression of effective recruitment rates. This study emphasizes the importance of predation on early life stages of basal species and the influence of seascapes on top-down interactions between subtidal predators and their intertidal prey.

Effects of eutrophication, grazing, and algal blooms on rocky shores

Eutrophication can profoundly change rocky shore communities. These changes often cause the replacement of perennial, canopy‐forming algae such as Fucus spp. with annual, bloom‐forming algae such as Enteromorpha spp. Grazing, however, can counteract eutrophication by eliminating the annual algae’s susceptible recruits. We examine these generalizations across large scales. We use replicated “bioassay” experiments to compare the effects of eutrophication and grazing across four paired control versus eutrophied sites in the Northwest Atlantic and four eutrophied sites in the Baltic Sea in spring and summer. At each site, annual algal recruitment and grazing pressure were estimated using tiles seeded with Enteromorpha intestinalis propagules. Tiles were exposed for 3 weeks with grazers excluded or allowed access. Productivity of E. intestinalis recruits was strongly related to eutrophication (10‐fold increase) and grazing (80% decrease) and was weakly related to season. While the absolute grazing rate increased in a linear fashion with algal productivity, the relative grazing rate remained surprisingly constant (;80%). Comparative field surveys showed that perennial algae decreased by 30–60%, while annual algae, filter feeders, and grazers increased across a gradient of eutrophication. As eutrophication increased from control to eutrophied to point source sites, rocky shore communities became increasingly dominated by single species of annual algae or filter feeders, and community diversity declined consistently by 24–46%. We conclude that grazers are important controllers of algal blooms but that, ultimately, they cannot override the effects of increasing eutrophication on rocky shore community structure and biodiversity.